• Polymer(Korea)
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• v.30 no.6
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• pp.464-470
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• 2006

Diblock copolymers consisting of methoxy Poly (ethylene glycol) (MPEG) and poly (${\epsilon}-ca$ prolactone) (PCL), poly(${\delta}-valerolactone$) (PVL), poly(L-lactide) (PLLA), or poly(L-lactide-co-glycolide) (PLGA) were prepared to compare the characterization of diblock copolymers as a drug carrier. MPEG-PCL, MPEG-PVL, MPEG-PLLA, and MPEG-PLGA diblock copolymers were synthesized by the ring-opening polymerization of ${\epsilon}$-caprolactone or ${\delta}$-valerolactone in the presence of $HCl{\cdot}Et_2O$ as a monomer activator at room temperature and by the ring-opening polymerization of L-lactide or a mixture of L-lactide and glycolide in the presence of stannous octoate at $130^{\circ}C$, respectively. The synthesized diblock copolymers were characterized with $^1H-NMR$, GPC, DSC, and XRD. The micellar characterization of MPEG-polyester diblock copolymers in an aqueous phase was carried out by using NMR, dynamic light scattering, AFM, and fluorescence techniques. Most micelles exhibited a spherical shape in AFM. Thus, ore confirmed that the micelles formed with MPEG-polyester diblock copolymers have possibility as a potential hydrophobic drug delivery vehicle because a hydrophobic drug could be preferentially distributed in the micelle core.

• Korean Journal of Microbiology
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• v.36 no.2
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• pp.155-160
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• 2000

Pseudomnas sp. HJ-2 is capable of producing a rubber-elastic polyhydroxyalkanoate (PHA) consisting of 3- hydroxybutyrate (3HB), 3-hydroxyvalerate (3HV), and 3-hydroxyheptanoate (3HHp) from heptanoic acid as the sole carbon source. The polyester produced was a blend of poly(3HB-co-3HV) and poly(3HHp). Although the mixing of poly(3HHp) fraction to poly(3HB-co-3HV) resulted in a decrease of modulus, the sole fraction of poly(3HB-co-3HV) with a high molar fraction of 3HV was shown to be an elastomer with the maximum percent strain of 740%. The biomass yield and the PHA synthesis were relatively high when the initial heptanoic acid concentration was 40 mM, and were significantly decreased when the substrate concentration exceeded 50 mM. The accumulation of PHA was stimulated by deficiency of nitrogen and phosphorus in the medium. The PHA contents and its monomeric compositions were greatly affected by pH and oxygen transfer rate. At pH 7.5, poly(3HB-~0.38% 3HV) was produced from heptanoic acid and a mixture of 95% 3HHp and 5% 3HV was produced at pH 8.0. Increased conten1 of 3HHp in the polyesters with lhe increasing oxygen transfer rate by agitation speed a1 a fixed aeration rate was observed.

• KSBB Journal
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• v.9 no.3
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• pp.246-252
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• 1994

Enzyme-catalyzed polycondensatlon reaction of aliphatic polyesters with several repeating units was studied using the biocatalytic activities of lipases from different sources. Porcine pancreatic lipase (PPL) was found to be best in utilizing bls(2,2,2-trichloroethyl) glutarate and 1,4-butanediol as substrafes. The reaction was also catalyzed to some extent by the lipases from Humicola lanuginos and Psudomonas sp. In the series of short-chain diols(C2-C4), bis(2,2,2-trichloroethyl) glutarate was iransesterified fastest with 1,4-butanediol and for the long-chain diols (PEG-300-PEG-1000), the reaction was fastest with PEG-400. With PEGs, only monoesterification product was obtained. PPL functioned well in relatively hydrophilic organic solvents such as tetrahydrofuran(THF), ether and acetonitrile. The reaction rate was accelerated as the reaction temperature was raised from $20^{\circ}C$ to $60^{\circ}C$ while Mn values of the reaction products were not affected by the reaction temperature. End group analysis by NMR showed that Mn values of the polymer were in the range of 1500-4000 daltons.

• Journal of Adhesion and Interface
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• v.19 no.3
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• pp.113-117
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• 2018

Boron carbide is lower in hardness than diamond or boron nitride but has a hardness of more than 30 GPa and is used for manufacturing tank armors and ammo shells due to its high hardness. It is also used as a neutron absorber due to its ability to absorb neutrons, which is increasing its use in nuclear power projects. Neutrons have no interaction with electrons and are known to pass through the material without interactions. Along with boron carbide, the atoms with high interaction with neutrons are hydrogen, and high hydrogen concentration polyesters and epoxy polymers including boron are used as materials for manufacturing products for nuclear power generation waste. In this paper, the surface of boron carbide is treated with iron oxide and tungsten to improve interaction between modified boron carbide and epoxy polymer. XRD and XPS were used to confirm that iron oxide and tungsten are well attached on the surface of boron carbide, respectively. The mechanical strength of the surface treated boron carbide was measured by a universal testing machine (UTM) and the dynamic characteristics of the cured product were observed by using a dynamic analyzer (DMA).

• KSBB Journal
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• v.22 no.6
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• pp.371-377
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• 2007

Polyhydroxyalkanoates (PHAs) are a family of microbial polyesters that can be produced by fermentation from renewable resources. PHAs can be used as completely biodegradable plastics or elastomers. In this paper, novel applications of PHAs in biosensor are described. A general platform technology was developed by using the substrate binding domain (SBD) of PHA depolymerase as a fusion partner to immobilize proteins of interest on PHA surface. It could be shown that the proteins fused to the SBD of PHA depolymerase could be specifically immobilized onto PHA film, PHA microbead, and microcontact printed PHA surface. We review the results obtained for monitoring the specific interaction between the SBO and PHA by using enhanced green fluorescent protein, red fluorescent protein, single chain antibody against hepatitis B virus preS2 surface protein and severe acute respiratory syndrome coronavirus surface antigen as model proteins. Thus, this system can be efficiently used for studying protein-protein and possibly protein-biomolecule interactions for various biotechnological applications.

• Polymer(Korea)
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• v.28 no.3
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• pp.211-217
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• 2004

The sol to gel transition of aqueous solution of block copolymers consisting of methoxy poly (ethylene glycol) (MPEG) and biodegradable polyesters such as $\varepsilon$-caprolactone and L-lactide was investigated as a function of temperature. MPEG-PCL was prepared by ring opening polymerization of $\varepsilon$-caprolactone in the presence of HClㆍEt$_2$O as monomer activator at room temperature. Also, MPEG-PLLA was prepared by ring opening polymerization of L-lactide in the presence of stannous octoate at 115$^{\circ}C$. The properties of block copolymers were investigated by $^1$H-NMR, IR, and GPC as well as the observation of thermo sensitive phase transition in aqueous solution. As the hydrophobic block length increased, the sol to gel transition temperature increased and curve of that steepen to lower concentration. To confirm the gel formation at body temperature, we observed the formation of gel in the mice body after injection of 20 wt% aqueous solution of each block copolymer. After surging, we investigated the gelation in mice. The results obtained in this study confirmed the feasibility as biomaterials of injectable implantation for controlled release of drug and protein delivery.

• Korean Journal of Microbiology
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• v.41 no.3
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• pp.225-231
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• 2005

The characteristics of cell growth and medium-chain-length polyhydroxyalkanoate (MCL-PHA) biosynthesis of Pseudomonas chlororaphis HS21 were investigated using plant oils as the carbon substrate. The organism was efficiently capable of utilizing plant oils, such as palm oil, corn oil, and sunflower oil, as the sole carbon source for growth and MCL-PHA production. When palm oil (5 g/L) was used as the carbon source, the cell growth and MCL-PHA accumulation of this organism occurred simultaneously, and a high dry cell weight (2.4 g/L) and MCL-PHA ($40.2\;mol{\%}$ of dry cell weight) was achieved after 30 hr of batch-fermentation. The repeating unit in the MCL-PHA produced from palm oil composed of 3-hydroxyhexanoate ($7.0\;mol{\%}$), 3-hydroxyoctanoate ($45.3\;mol{\%}$), 3-hydroxydecanoate ($39.0\;mol{\%}$), 3-hydroxydodecanoate ($6.8\;mol{\%}$), and 3-hydroxytetradecanoate ($1.9\;mol{\%}$), as determined by GC/MS. Even though glucose was a carbon substrate that support cell growth but not PHA production, the conversion rate of palm oil to PHA was significantly increased when glucose was fed as a cosubstrate, suggesting that bioconversion of some functionalized carbon substrates to related polymers in P chlororaphis HS21 could be enhanced by the co-feed of good carbon substrates for cell growth. In addition, the change of compositions of repeating units in MCL-PHAs synthesized from the plant oils was markedly affected by the supplementation of acrylic acid, an inhibitor of fatty acid ${\beta}-oxidation$. The addition of acrylic acid resulted in the increase of longer chain-length repeating units, such as 3-hydroxydodecanoate and 3-hydroxytetradecanoate, in the MCL-PHAs produced. Particularly, MCI-PHAs containing high amounts of unsaturated repeating units could be produced when sunflower oil and corn oil were used as the carbon substrate. These results suggested that the alteration of PHA synthesis pathway by acrylic acid addition can offer the opportunity to design new functional MCL-PHAs and other unusual polyesters that have unique physico-chemical properties.

• Applied Chemistry for Engineering
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• v.31 no.2
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• pp.115-124
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• 2020

Sustainable plastics can be mainly categorized into (1) biodegradable plastics decomposed into water and carbon dioxide after use, and (2) biomass-derived plastics possessing the carbon neutrality by utilizing raw materials converted from atmospheric carbon dioxide to biomass. Recently, biomass-derived engineering plastics (EP) and natural nanofiber-reinforced nanocomposites are emerging as a new direction of the industry. In addition to the eco-friendliness of natural resources, these materials are competitive over petroleum-based plastics in the high value-added plastics market. Polyesters and polycarbonates synthesized from isosorbide and 2,5-furandicarboxylic acid, which are representative biomass-derived monomers, are at the forefront of industrialization due to their higher transparency, mechanical properties, thermal stability, and gas barrier properties. Moreover, isosorbide has potential to be applied to super EP material with continuous service temperature over 150 ℃. In situ polymerization utilizing surface hydrophilicity and multi-functionality of natural nanofibers such as nanocellulose and nanochitin achieves remarkable improvements of mechanical properties with the minimal dose of nanofillers. Biomass-derived tough-plastics covered in this review are expected to replace petroleum-based plastics by satisfying the carbon neutrality required by the environment, the high functionality by the consumer, and the accessibility by the industry.